1. Field of the Invention
Most conventional lawnmowers cut the lawn using one or more large metal blades rotating in a plane of rotation that is substantially parallel to the land surface beneath the grass being mowed. Additionally, most conventional lawnmowers have some type of blade height adjustment. Blade height adjustments are typically achieved by raising or lowering the lawnmower chassis relative to the land surface, and may require a fair amount of time and additional tools. These adjustments can be used to reduce the power required to cut the lawn by raising the blade. However, once a blade height is selected the height and thickness of the lawn and the velocity in which the mower is moved through the lawn determine the blade's cutting area and commensurate amount of power required by the lawnmower. To accommodate the wide variety of grass heights and densities while providing for adequate speed of forward movement to satisfy the user, most lawnmowers are powered by internal combustion engines of significant horsepower. Moreover, mowers utilizing a plurality of large blades, such as riding mowers or large-swath mowers towed by a tractor, typically require gearing mechanisms to achieve increased speeds, and may become bogged down and stall in high, dense grass at high speeds.
Electric motors of equal horsepower are also used to power conventional lawnmowers, but finding an efficacious power source to drive such electric motors has proven challenging. For instance, the batteries required to supply enough power for an adequate mowing time are typically prohibitive in size, weight and expense, while the typical home (20-amperes) circuit restricts power supplied by a power cord. Furthermore, a cord also restricts ease of movement of the lawnmower, as well as the distance the mower can travel from the outlet into which the cord is plugged.
The combination of one or more large blades and a powerful internal combustion engine or electric motor also presents a safety hazard, since the blade is capable of cutting with significant force. A further drawback is the relatively large size and weight of lawnmowers utilizing a powerful internal combustion engine or large electric motor, which reduces the ease of lawnmower operation and storage. With respect to lawnmowers powered by internal combustion engines, a further drawback is that the user typically incurs the cost of purchasing oil and gasoline or other flammable fuel and stores it at his or her home in volumes adequate to fuel the mower for a number of uses, creating a potential fire hazard at the home. Internal combustion engines also produce carbon dioxide emissions which may have a negative impact on air quality and the environment. Finally, when conventional lawnmower blades become periodically dulled and in need of replacement, the blade replacement process may be quite cumbersome to the average user, requiring substantial time and additional tools.
2. Description of the Related Art
U.S. Pat. No. 3,070,938 (“the '938 patent) discloses a lawnmower comprising a plurality of individual blade units that operate together as a unit in order to cut a wider swath than mowers existing in the art at the time of the invention embodied therein. The apparatus disclosed in the '938 patent was designed for attachment to a tractor or other powered vehicle and was designed to be raised and lowered in order to follow the topography of the land surface being mowed. While the planes of rotation of the plurality of blades described in the '938 patent are not at all times perfectly parallel to the land being mowed when the mower is in use, they do remain substantially parallel to the land surface, and the cutting area of each blade of the invention embodied in the '938 patent is thus greater than that of the blades used in the present invention. The reduction in cutting area is a significant feature of the present invention inasmuch as the amount of power required is reduced as compared to the plurality of blades used in the invention disclosed in the '938 patent. This enables the use of alternative power sources such as batteries in the present invention to power the cutting blades while an internal combustion engine powering a separate vehicle is required in order to enable the invention of the '938 patent.
U.S. Pat. No. 5,761,892 (the '892 patent) discloses a rotary blade for a rotary lawnmower that provides an equivalent cut to the invention of the '938 patent with a reduction in necessary driving power. The reduction of power described in the invention of the '892 patent is achieved by affixing a plurality of individual cutting elements to a single support arm rotating about a single rotary drive shaft, each cutting element of sufficient length and projecting downward at a suitable angle such that the cutting elements cut the grass as the support arm rotates at a height above the grass. The present invention differs from that embodied in the '892 patent because each of the plurality of blades has its own drive shaft and the drive shafts are situated at an angle tilted longitudinally between 1 and 90 degrees from vertical. Moreover, each drive shaft of the present invention may be powered by an individual motor that uses only the power necessary to power the blade affixed thereto to cut the grass in its cutting path, thereby increasing the overall efficiency of the apparatus as a whole by requiring only the energy actually necessary to cut the grass in the path of each discrete member of the plurality of blades.